This invention relates to a balancer structure for a V-type engine, and more particularly to a balancer structure for a V-type engine in which a balancer shaft is arranged in closest proximity to a crankshaft which is a source of vibration, so that inertial couple-forces are effectively canceled to reduce vibration.
Some V-type engines have first and second cylinder banks defining a banking angle of 60 degree or 90 degree therebetween. A 60-degree V8-cylinder engine, that is a 60 degree banking angle and four cylinders in each cylinder bank, is not generally used as compared to a 90-degree V8-cylinder engine having a banking angle set at 90 degree and four cylinders in each cylinder bank. This is due to the fact that in the 90-degree V8-cylinder engine primary and secondary inertial forces or couple forces are well balanced by optimally setting a counterweight of a crankshaft, while in the 60-degree V8-cylinder engine primary inertial couple forces remain as residual unbalance.
One system, in which the balancer shaft cancels the vibration occurring from inertial force or couple forces in the crank system, is a balancer structure for a V-type engine having a balancer shaft in parallel with a crankshaft. This balancer structure for the V-type engine cancels vibration by rotating the balancer shaft in synchronization with the crankshaft and in a normal or reverse direction therewith, so that the primary and secondary inertial forces or inertial couple forces are balanced. Examples of such balancer structures for the V-type engine are disclosed in Japanese Laid-Open Patent No. 4-290639 and Japanese Laid-Open Patent No. 63-125840.
According to Japanese Laid-Open Patent No. 4-290639, a V-type engine includes a single balancer shaft in parallel with a crankshaft and having an eccentric weight. The balancer shaft toward the front of the engine which is rotated by the crankshaft, is disposed below the crankshaft and toward the side of the engine where fewer auxiliary machineries are installed. An oil pump driven through the balancer shaft is disposed toward the above-mentioned side in an oil pan below the balancer shaft. An oil filter is also arranged toward the above side.
According to Japanese Laid-Open Patent No. 63-125840, a V-type engine with eight cylinders has a banking angle set at an angle of 60 degree. A single balancer shaft rotates in the same direction as the crankshaft at a speed twice as fast as that of the crankshaft. The balancer shaft has the rotating axis thereof eccentrically (i.e. sidewardly) offset from the center axis of the crankshaft. Accordingly, rolling moment created by the piston pressure is reduced.
As previously mentioned, the 60-degree V8-cylinder engine is not generally used, since in the 90-degrees V8-cylinder engine primary and secondary inertial forces or couple forces are well balanced by optimally setting a counterweight of a crankshaft, while in the 60-degree V8-cylinder engine primary inertial couple forces remain as residual unbalance.
Some 60-degree V8-cylinder engines have a balancer structure including a balancer shaft which is driven by a chain and the like in a space between the cylinder banks to cancel or reduce the inertial couple forces. However, in the balancer structure having the balancer shaft in the space between cylinder banks, the balancer shaft is disposed away from the crankshaft which generates the vibration. Accordingly, it is not adequate for canceling the forces to a sufficient degree, so that the vibration cannot be reduced effectively.
In addition, since the balancer shaft is disposed away from the crankshaft which generates the vibration in this balancer structure for the V-type engine, and the couple forces are proportional to the distance therebetween, the balancer shaft is required to be heavier in proportion to the distance. Also, the larger and heavier balancer shaft as positioned away from the crankshaft and the larger space for mounting the balancer shaft result in a larger and heavier V-type engine.
In order to obviate or minimize the above problem, the present invention provides a balancer structure for a V-type internal combustion engine having a balancer shaft supported in parallel with a crankshaft. The balancer shaft is positioned on the center plane which divides the cylinder banks of the V-type engine and which passes through an axis of the crankshaft, and is positioned directly below the crankshaft.
According to the present invention, the balancer shaft is positioned on the center plane which divides the cylinder banks of the V-type engine and which passes through the axis of the crankshaft, and is positioned directly below the crankshaft. The balancer shaft can be positioned closer to the crankshaft generating vibration to shorten the distance between the crankshaft and the balancer shaft.